Zilog in a matchbox

Now you can have a Zilog computer in the form factor of a matchbox. The RamBlade is a tiny PCB that uses a Parallax Propeller IC to implement the CP/M language. The OS is stored on a microSD card, with a four-pin serial interface (3V3, GND, SO, SI) that allows operation via a terminal program.

I’ve been watching this project unfold on the Propeller forums. Yes, it’s a software emulation of a Z80 and a complete Z80 I/O system including disks and UARTs (and, in other form factors, modern keyboard and video). While the hardware tech isn’t old the key is that the software tech really is; it’s a complete functioning CP/M system supporting all the compilers and dev tools that were around in the 1970’s. It’s a pure trip into the past, much more useful than it has any right to be, and the original hardware was more suitcase than matchbox sized.

As the original author of “ZiCog” I have to put some things straight here.
ZiCog is a software emulation of a Zilog Z80 8-bit processor written in assembler for the Parallax Inc. Propeller micro-controller. It runs Z80 code at about the same rate as the original chip. Together with some peripheral hardware simulation it runs the CP/M operating system from an SD or micro SD card acting as floppy/hard disk storage. With 64K of external RAM attached it has enough space to run the WordStar word processor and many language compilers and interpreters of the 8-bit era. Including MicroSofts BASIC.
Many people have contributed software and hardware ideas as well as actual hardware constructions to this effort. What you see here is the smallest of them so far, by Cluso. As far as we know it is the smallest complete CP/M computer in the world.

CP/M is an OS, not a language (ah, CALL BDOS!).
Zilog is the foundry for the Z80 processor, and it was still very much alive in the 80’s (http://en.wikipedia.org/wiki/CP/M).

It reminds me of those poorly written articles in newspapers, where you can read stuff like: the pilot of a small Cessna, a Piper PA-28, landed on a golf course… Any aviation enthusiast can catch this one.

Zilog is still alive and kicking and they can still sell you a processor that will run the Z80 instruction set. However I don’t think you can build a smaller CP/M computer even with modern chips from Zilog:)

I’ve made a couple SBCs from Zilog chips over the years, last one had less component mesh and the 20MHZ chip. They are fun to program and learn assembler and real mode, the propeller I think can do assembler too but it has a locked ROM. It’s be just as easy to do this with an actual Zilog processor, but you’d need controllers for some stuff.

As designer of the hardware, let me explain the RamBlade…
* Propeller chip, 8 processor cores, each with 2KB RAM, and 32KB shared RAM. 80MHz but will be overclocked above 100MHz.
* 64KB I2C EEPROM for up to 32KB prop boot code.
* 512KB 55nS SRAM chip.
* microSD up to 2GB.
* 2 I/O pins used for serial to an external terminal or PC. An alternative modification (using a few resistors and capacitor) for connecting a PS2 Keyboard and Composite Video (80×25) direct to the RamBlade is a WIP.
* An optional onboard 3V3 regulator may be fitted. Requires an external power supply.
* ZiCog software (Z80+Interface emulation) runs CPM2.2 and can run CPM3 (banked switching WIP).
* CPM2.2 has been configured for up to 8 x 8MB hard drives on the microSD card.
* At 80MHz it runs faster than a real Z80 at 4MHz.
* No external programmer required. Updates can be loaded from microSD files.
* Able to run other software besides Z80/CPM, including Propeller and Basic (WIP). 6502 and 6809 emulators are WIP.

tj: Actually it is EASIER to use a Propeller and ZiCog emulation than a real Z80.

One can use a single 40 pin DIP Propeller MCU and a 64K RAM chip to emulate the Z80, the console I/O, the floppy/hard disks AND the Video display (80 * 26 chars). Complete CP/M system the size of a cigarette packet on a home made PCB all solderable by hand.

The board in the above link is the DIP package version and is self contained with vga driver, keyboard driver, hard drive etc all on one board. The propeller can do graphics too (even Castle Wolfenstein).

And other chips can be emulated too – it is just a matter of going though each instruction and making sure the flags are set correctly and that it does what it is supposed to.